The exact determination of product temperature in mixing and kneading machines is of increasing importance due to progressive automation and to the processing of temperature sensitive products.
The temperature sensors currently utilized in practice in mixing and kneading machines have a measurement error of 10 to 20% or more and consist of a number of individual parts. Due to severe operational conditions and the high mechanical stresses in mixing and kneading tanks, temperature sensors must be made very stable particularly at the measurement tip which is immersed in the mixed material. Temperature sensors therefore are utilized either with or without measurement tips that are insulated with respect to the sensor housing.
In the case of non-insulated measurement tips, there is a high transfer of heat from the measurement tip to the housing and in this way there arises a relatively large measurement error.
In the case of insulated measurement tips, many individual parts are necessary. The measurement tip only has a shallow immersion depth, since it can only be relatively small with respect to the sensor housing, due to the insulation necessary between the measurement tip and the sensor housing. The shallow immersion depth and thus the small wetted surface of the measurement tip causes measurement errors.
A temperature sensor for rubber kneaders equipped with insulated measurement tips is described in DE - GM 19 35 219. The measurement tip (measurement value sensor) is surrounded by one or more elements having a low heat conductivity and by two receiving bushings. In addition, an elastic gasket, a pressure unit, and a receiving shaft are necessary to complete the construction of the temperature sensor. In addition to the large number of individual components, which imposes a high cost of manufacture and assembly for such temperature sensors, the necessary pressure sealing is for the most part not obtained or not obtained permanently.